For example, in electrophotography, an electrostatic image bearing member comprising a photoconductive photosensitive member is charged and exposed to light to form an electrostatic latent image thereon, then the electrostatic latent image is developed with a toner formed in fine particles by having colorants, etc. contained in a binder comprising a resin, and the toner image obtained is transferred onto a support such as a transfer paper, followed by fixing, to form a visible image.
Thus, in order to obtain a visible image, it is necessary to fix a toner image, and hot roller fixing system, which is high in thermal efficiency and capable of high speed fixing, has been widely employed in the prior art.
Whereas, in these days, for such demands as (a) suppresion of overheating of copying machine, (b) prevention of thermal deterioration of photosensitive member, (c) shortening of warm-up time required to elevation of temperature of hot roller to a temperature capable of fixing from the beginning of actuation of fixer, (d) feasibility of continuous copying for a large number of times by making lowering in temperature of hot roller due to absorption of the heat to transfer paper smaller, (e) enhanced thermal stability, etc., it has been strongly required to enable fixing treatment under the state where the temperature of the hot roller is made lower by lowering the consumed power of the heater for fixing. Accordingly, the toner is also required to be fixable well at a lower temperature.
Besides, a toner is required to be capable of existing stably as powder without agglomeration under the conditions during use or under the storage environment, namely excellent in anti-blocking property. Further, in the hot roller fixing system, which is preferred as the fixing method, since the off-set phenomenon, namely the phenomenon wherein a part of the toner constituting the image during fixing is transferred onto the hot roller and retransferred onto the next transfer paper delivered to stain the image, is liable to occur, it is required to impart to the toner a performance which can prevent generation of off-set phenomenon, namely off-set resistance.
For such reasons, in the prior art, there have been proposed a technique in which a polymer comprising at least one crystallizable polymer portion with a melting point of 45.degree. to 150.degree. C. and an amorphous polymer portion with a glass transition point of 0.degree. C. or lower chemically linked together as is used as the binder resin constituting the toner, as disclosed in Japanese Unexamined Patent Publication No. 87032/1975, or a technique in which a thermoplastic polymer containing in its molecule a crystalline block with melting point of 50.degree. to 70.degree. C. and an amorphous block having a glass transition point higher by at least 10.degree. C. than the melting point of the crystalline block, with the content of the crystalline block being 70 to 95 wt.%, is used as the binder resin constituting the toner, as disclosed in Japanese Unexamined Patent Publication No. 3446/1984.
Also, Japanese Unexamined Patent Publication No. 8549/1982 discloses a toner containing a graft copolymer comprising a crystalline trank polymer portion comprising at least one monomer selected from ethylene, propylene and vinyl acetate; an unsatureted polyester trank polymer portion; and a vinyl type branch polymer portion.
However, in the technique disclosed in the above Japanese Unexamined Patent Publication No. 87032/1975, the toner, which is constituted of a copolymer having a crystalline polymer portion which is soft at normal temperature and an amorphous polymer portion which is sticky and soft due to the glass transition point of 0.degree. C. or lower chemically linked together, has the disadvantage that it may cause blocking phenomenon in a developing instrument, etc., even at normal temperature. Also, developing characteristic is bad due to poor triboelectric chargeability and flowability to give unclear images much in fog. Also, after a large number of copying, a soft toner will generate the filming phenomenon that the toner is attached on the carrier particles or the surface of the photosensitive member. Further, the toner becomes fused onto a cleaning member such as cleaning blade, etc., whereby the images become unclear with much fog and low density. Also, due to its softness, the toner is liable to be formed into a mass in a pulverizing machine during pulverization at normal temperature, thus having the disadvantages such that pulverization can be done with difficulty to give no toner with desired particle size to make the cost higher with poor production efficiency. Further, due to high stickiness, off-set phenomenon is liable to be generated on a hot roller fixer which is not coated with a large amount of oil.
On the other hand, in the technique disclosed in Japanese Unexamined Patent Publication No. 3446/1984, since an amorphous block having a high glass transition point of 100.degree. C. or higher is used, a large amount as 70 to 95 wt.% of a crystalline block must be used as a method to satisfy meltability at a low temperature, whereby the properties of the soft crystalline block having plastic deformability at normal temperature are reflected on the toner. That is, due to its softness, triboelectric chargeability and flowability are bad to make developing characteristic bad, whereby unclear images with much fog are obtained. Also, after a large number of copies are made, the toner will generate the filming phenomenon that the toner is attached on the carrier particles or the surface of the photosensitive member, and also triboelectric chargeability becomes bad and the toner is further fused onto a cleaning member such as cleaning blade, etc., whereby the images become unclear with much fog and low density. Further, in a fixing method by heating within a short time with the use of a hot roller fixer not coated with a large amount of oil, the fixable temperature becomes higher due to the high glass transition point of the above amorphous block of 100.degree. C., and also off-set phenomenon is liable to be generated due to much crystalline block which is 70 to 95 wt.%.
Further, the toner disclosed in Japanese Unexamined Patent Publication No. 8549/1982 is also bad in flowability, whereby no developer having toner uniformly dispersed in carrier can be formed and no sufficient triboelectric chargeability can be obtained to make developing characteristic poorer and generate image drop-off, thus giving unclear images. Further, in copying over a large number of times, due to bad flowability of the toner, the toner cannot be dispersed uniformly into the developer even when the toner may be supplemented, whereby the images become unclear.
The prior art has failed to provide a practical toner which avoids the disadvantages described above.